Method for improving alignment between selective emitter and metal printing

ABSTRACT

A method for improving alignment between a selective emitters and metal printing, including: providing silicon wafer including first edge and midline parallel to the first edge; texturing and diffusing surface of the silicon wafer; and illuminating the surface of the silicon wafer by laser spots to form the SE. Multiple laser spots are arranged between the first edge and the midline to form spot rows, extension directions of the spot rows are parallel to the first edge, M spot rows are arranged and M is a positive integer and M&gt;1. The M spot rows include N sub-spot regions, N is a positive integer and 1&lt;N≤M, the sub-spot regions include at least one spot row, and areas of the laser spots in each sub-spot region are equal. The areas of the laser spots in different sub-spot regions from the midline pointing to the first edge gradually increases.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to Chinese Patent ApplicationNo. 202210892920.3, filed on Jul. 27, 2022, the content of which isincorporated herein by reference in its entirety.

TECHNICAL FIELD

The present disclosure relates to the technical field of solar cells,and in particular, to a method for improving alignment between aselective emitter (SE) and metal printing.

BACKGROUND

In recent years, with the decline of fossil fuels and their negativeimpact on environments, research and utilization of solar energy aspollution-free and renewable energy have been rapidly developed.

With the continuous development of the photovoltaic industry, aphotovoltaic module has a greater demand for high-efficiency cells. Inindustrial production of the high-efficiency cells, an SE celltechnology has been widely used. An SE cell has a structure featuredwith heavy doping in a screen metal electrode contact region and lightdoping in a screen metal electrode non-contact region by using lasers.The structure can reduce diffusion layer coincidence, improve ashortwave effect of optical fibers, and increase a short-circuit currentand an open-circuit voltage.

In the manufacturing process of the SE cell, it is inevitable to balancealignment between laser spots and screen metal electrodes. For example,if the laser spots are larger, the heavily doped region is larger, so itis easier to align the metal electrodes with the light spots. However,excessively large laser spots may affect the open-circuit voltage of theSE cell and reduce power generation efficiency of the SE cell. If thelaser spots are smaller, higher precision of the alignment between themetal electrodes and the laser spots is required.

Therefore, it is urgent to provide a method for improving alignmentbetween an SE and metal printing.

SUMMARY

In view of the above, the present disclosure provides a method forimproving alignment between an SE and metal printing, including:providing a silicon wafer including a first edge and a midline, themidline is parallel to the first edge; texturing and diffusing a surfaceof the silicon wafer; and illuminating the surface of the silicon waferby laser spots to form the SE. A plurality of the laser spots arearranged along a first direction between the first edge and the midlineto form spot rows, extension directions of the spot rows are parallel toan extension direction of the first edge, M spot rows are arranged alonga second direction intersecting with the first direction, and M is apositive integer and M>1. The M spot rows include N sub-spot regionsarranged along the second direction, N is a positive integer and 1<N≤M,the sub-spot regions include at least one of the spot rows, and areas ofthe laser spots in each of the sub-spot regions are equal. The areas ofthe laser spots in different sub-spot regions along a direction from themidline pointing to the first edge gradually increases.

Other features of the present disclosure and advantages thereof willbecome clear from the following detailed description of exemplaryembodiments of the present disclosure with reference to the accompanyingdrawings.

BRIEF DESCRIPTION OF DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate embodiments of the presentdisclosure and, together with the description, serve to explain theprinciples of the present disclosure.

FIG. 1 shows a pattern of laser spots of an SE according to one or moreembodiments of the present disclosure;

FIG. 2 shows a pattern of laser spots of another SE according to one ormore embodiments of the present disclosure;

FIG. 3 shows a pattern of laser spots of yet another SE according to oneor more embodiments of the present disclosure;

FIG. 4 shows a pattern of laser spots of still another SE according toone or more embodiments of the present disclosure; and

FIG. 5 shows a pattern of laser spots of a further SE according to oneor more embodiments of the present disclosure.

DESCRIPTION OF EMBODIMENTS

Various exemplary embodiments of the present disclosure are nowdescribed in detail with reference to the accompanying drawings. Itshould be noted that, unless otherwise stated specifically, relativearrangement of the components and order of steps, the numericalexpressions, and the values set forth in the embodiments are notintended to limit the scope of the present disclosure.

The following description of one or more exemplary embodiments is infact merely illustrative, and shall not be construed as any limitationson the present disclosure and application or use thereof.

Technologies, methods, and devices known to those of ordinary skill inthe related art may not be discussed in detail, but where appropriate,such technologies, methods, and devices should be considered as part ofthe specification. In all the examples shown and discussed herein, anyspecific value should be construed as merely illustrative and not as anylimitation. Therefore, other examples of exemplary embodiments may havedifferent values.

It should be noted that similar reference signs and letters denotesimilar terms in the accompanying drawings, and therefore, once an itemis defined in a drawing, there is no need for further discussion in theaccompanying drawings.

Referring to FIG. 1 and FIG. 2 , FIG. 1 shows a pattern of laser spotsof an SE according to one or more embodiments of the present disclosure,and FIG. 2 shows a pattern of laser spots of another SE according to oneor more embodiments of the present disclosure, to describe a method forimproving alignment between an SE and metal printing. The methodincludes: providing a silicon wafer 1, the silicon wafer 1 includes afirst edge 2 and a midline 3, the midline 3 is parallel to the firstedge 2; texturing and diffusing a surface of the silicon wafer 1;illuminating the surface of the silicon wafer 1 by laser spots 4 to formthe selected emitter, between the first edge 2 and the midline 3, aplurality of the laser spots 4 is arranged along a first direction X toform spot rows 5, extension directions of the spot rows 5 are parallelto an extension direction of the first edge 2, M spot rows 5 arearranged along a second direction Y, M is a positive integer and M>1,the second direction Y intersects with the first direction X; the M spotrows 5 includes N sub-spot regions 6 arranged along the seconddirection, N is a positive integer and 1<N≤M, the sub-spot regions 6includes at least one of the spot rows 5, and areas of the laser spots 4in each of the sub-spot regions 6 are equal; and gradually increasingthe areas of the laser spots 4 in different sub-spot regions 6 along adirection from the midline 3 pointing to the first edge 2.

It is to be noted that the midline 3 herein is not an actual line on thesilicon wafer 1. The midline 3 is a dummy line. A silicon wafer 1 isprovided, and the silicon wafer 1 may be monocrystalline silicon,polycrystalline silicon, or amorphous silicon. In some embodiments,monocrystalline silicon is adopted. The surface of the silicon wafer 1is textured and diffused. Prior to the texturing, the surface of thesilicon wafer 1 is cleaned to remove impurities from the surface of thesilicon wafer 1. A pyramid structure is formed on the surface of thesilicon wafer 1 during the texturing, so as to reduce reflectivity ofthe surface of the silicon wafer 1. The textured silicon wafer 1 isdiffused to form a PN junction. The diffused silicon wafer 1 is heavilydoped by using laser spots 4. Areas of the laser spots 4 determine thesize of the SE.

It may be understood that, referring to FIG. 1 and FIG. 2 , FIG. 1 andFIG. 2 illustrate only a pattern of laser spots 4 between the first edge2 and the midline 3. In FIG. 1 , each sub-spot region 6 includes atleast two spot rows 5, and FIG. 2 only illustrates that each sub-spotregion 6 includes only one spot row 5, which is not limited thereto. Thenumber of the sub-spot region 6, the number of the spot row 5 includedin the sub-spot region 6, the number of the laser spots 4 included inthe spot row 5, an interval between two adjacent laser spots 4, aspacing between two adjacent spot rows 5, and a spacing between twoadjacent sub-spot regions 6 in FIG. 1 and FIG. 2 are merelyillustrative, and are not limited thereto. Alternatively, one part ofthe sub-spot regions 6 include only one spot row 5, while the other partof the sub-spot regions 6 include at least two spot rows 5, which is notlimited in the present disclosure, provided that the areas of the laserspots 4 in different sub-spot regions 6 are gradually increased alongthe direction from the midline 3 pointing to the first edge 2. Thecloser to the edge position of the silicon wafer 1, the larger the areaof the laser spot 4, which is helpful to realize accurate alignmentbetween the metal electrode and the SE when the metal electrode deviatesgreatly.

Compared with the related art, the method for improving alignmentbetween an SE and metal printing according to the present disclosure hasat least the following advantages.

In the method for improving alignment between an SE and metal printingaccording to the present disclosure, between the first edge 2 and themidline 3, a plurality of the laser spots 4 are arranged along a firstdirection X to form spot rows 5, extension directions of the spot rows 5are parallel to an extension direction of the first edge 2, M spot rows5 are arranged along a second direction Y, where M is a positive integerand M>1, and the second direction Y intersects with the first directionX. The M spot rows 5 include N sub-spot regions 6 arranged along thesecond direction Y, where N is a positive integer and 1<N≤M. Thesub-spot regions 6 include at least one of the spot rows 5, and areas ofthe laser spots 4 in each of the sub-spot regions 6 are equal. The areasof the laser spots 4 in different sub-spot regions 6 are graduallyincreased along a direction in which the midline 3 points to the firstedge 2. The metal electrode is generally printed by a screen. Due tobonding of hot melt adhesive at edges of the screen and prolonging ofthe service life, the metal electrode at an edge position may deviate.That is, the position of the metal electrode at the edge changesgreatly, while the position of the metal electrode in the middle changeslittle. Therefore, by designing the area of the laser spot 4 at a middleposition to be small and the area of the laser spot 4 at an edgeposition to be large, contact resistance of contact between the siliconwafer 1 and the SE at the middle position can be reduced, a fill factorcan be increased, and efficiency of a solar cell can be improved.Besides, when the service life of the screen is prolonged, the metalelectrode at the edge position and the SE at the edge position areaccurately aligned.

In some embodiments, still referring to FIG. 2 , each sub-spot region 6includes only one spot row 5.

It may be understood that each sub-spot region 6 includes only one spotrow 5, areas of the laser spots 4 in each sub-spot region 6 are equal,and the areas of the laser spots 4 in different sub-spot regions 6 aregradually increased along a direction from the midline 3 pointing to thefirst edge 2. That is, the areas of the laser spots 4 of each spot row 5are gradually increased along the direction from the midline 3 pointingto the first edge 2. The gradient areas of the laser spots 4 can furtheradapt to gradual deviation of the metal electrode and ensure accuracy ofthe alignment between the metal electrode and the SE, and can alsoensure reduction of the contact resistance of the contact between thesilicon wafer 1 and the SE at the middle position, increase of the fillfactor, and thereby improving the efficiency of the solar cell.

In some embodiments, still referring to FIG. 1 , each sub-spot region 6includes at least two spot rows 5.

It may be understood that each sub-spot region 6 includes at least twospot rows 5, areas of the laser spots 4 in each sub-spot region 6 areequal, and the areas of the laser spots 4 in different sub-spot regions6 are gradually increased along the direction from the midline 3pointing to the first edge 2. That is, sizes of the laser spots 4 aredesigned regionally along the direction from the midline 3 pointing tothe first edge 2, so as to more adapt to deviation of the metalelectrode only at the edge position, which can ensure minimum contactresistance between the silicon wafer 1 and the SE at the middleposition, thereby improving the efficiency of the solar cell.

In some embodiments, referring to FIG. 3 , FIG. 4 , and FIG. 5 , FIG. 3shows a pattern of laser spots of yet another SE according to one ormore embodiments of the present disclosure, FIG. 4 shows a pattern oflaser spots of still another SE according to one or more embodiments ofthe present disclosure, and FIG. 5 shows a pattern of laser spots of afurther SE according to one or more embodiments of the presentdisclosure. The silicon wafer 1 further includes a second edge 7. Thesecond edge 7 is arranged opposite to the first edge 2 along the seconddirection Y.

Between the second edge 7 and the midline 3, the plurality of laserspots 4 are arranged along the first direction X to form spot rows 5,and P spot rows 5 are arranged along the second direction Y, where P isa positive integer and P>1.

The P spot rows 5 include Q sub-spot regions 6 arranged along the seconddirection Y, where Q is a positive integer and 1<Q≤P, the sub-spotregions 6 include at least one of the spot rows 5, and areas of thelaser spots 4 in each of the sub-spot regions 6 are equal.

The areas of the laser spots 4 in the sub-spot regions 6 are graduallyincreased along a direction from the midline 3 pointing to the secondedge 7.

It may be understood that FIG. 3 only illustrates that each sub-spotregion 6 includes at least two spot rows 5 between the second edge 7 andthe midline 3, and FIG. 4 and FIG. 5 only illustrate that each sub-spotregion includes only one spot row 5 between the second edge 7 and themidline 3. That is, a pattern of the laser spots 4 between the firstedge 2 and the midline 3 is different from a pattern of the laser spots4 between the second edge 7 and the midline 3, which is not limitedthereto. Alternatively, between the second edge 7 and the midline 3, onepart of the sub-spot regions 6 include only one spot row 5, while theother part of the sub-spot regions 6 include at least two spot rows 5,which is not limited in the present disclosure. The areas of the laserspots 4 in the sub-spot regions 6 are gradually increased along thedirection from the midline 3 pointing to the first edge 2, and the areasof the laser spots 4 in the sub-spot regions 6 are gradually increasedalong the direction from the midline 3 pointing to the second edge 7.When the metal electrodes at the first edge 2 and the second edge 7 bothdeviate, the metal electrodes at the first edge 2 and the second edge 7can accurately contact the SE, while the center of the silicon wafer 1maintains small contact resistance with the SE.

In some embodiments, still referring to FIG. 3 and FIG. 4 , the laserspots 4 between the midline 3 and the first edge 2 form a first spotregion 8, the laser spots 4 between the midline 3 and the second edge 7form a second spot region 9, and the first spot region 8 and the secondspot region 9 are symmetric along the midline 3.

It may be understood that, since the silicon wafer 1 is symmetric alongthe midline 3, the symmetry of the first spot region 8 and the secondspot region 9 along the midline 3 is more reasonable, brings a betteralignment effect, and achieves higher efficiency of the solar cell.

In some embodiments, still referring to FIG. 1 to FIG. 5 , the laserspots 4 are circular.

It may be understood that orthographic projections of the laser spots 4on the silicon wafer 1 are circular, and the areas of the laser spots 4can be changed by changing diameters of the laser spots 4.

In some embodiments, the laser spots 4 may also be rectangular,equilaterally polygonal, or the like. When the laser spots 4 are oblong,lengths and widths of the laser spots 4 can be increased simultaneouslyto increase the areas of the laser spots 4. The lengths and the widthsof the laser spots 4 have a linear relationship.

In some embodiments, printing speeds of lasers on the silicon wafer 1,laser power, laser frequencies, and focal lengths of a lens throughwhich the lasers are emitted are adjusted to adjust the diameters of thelaser spots 4.

It may be understood that the sizes of the laser spots 4 may be changedby changing relative positions of lenses in a device from which thelasers are emitted, or by cooperatively adjusting printing speeds, laserpower, laser frequencies, and focal lengths of lenses through which thelasers are emitted. The focal lengths of the lenses through which thelasers are emitted may be adjusted by shifting positions of the lensesthrough which the lasers are emitted to change positions of focuses.

In some embodiments, for the laser spot 4 far from the midline 3, theprinting speed ranges from 20000 mm/s to 24000 mm/s, the laser powerranges from 29 W to 31 W, the laser frequency ranges from 230 KHZ to 270KHZ, and the focal length ranges from 30000 mm to 38000 mm.

It may be understood that, by setting the above parameters, thediameters of the laser spots 4 may be increased. That is, the laserspots 4 may be formed near the first edge 2 and/or the second edge 7 byusing the above parameters.

In some embodiments, for the laser spot 4 close to the midline 3, theprinting speed ranges from 20000 mm/s to 24000 mm/s, the laser powerranges from 28 W to 30 W, the laser frequency ranges from 270 KHZ to 330KHZ, and the focal length ranges from 28000 mm to 35000 mm.

It may be understood that, by setting the above parameters, thediameters of the laser spots 4 formed are small. That is, the laserspots 4 may be formed near the midline 3 by using the above parameters.

In some embodiments, the diameters of the laser spots 4 range from 35 μmto 130 μm.

It may be understood that, the diameters of the laser spots 4 constantlyincrease along the midline 3 toward the first edge 2 and/or the secondedge 7. That is, the diameters of the laser spots 4 near the midline 3are 35 μm, and the diameters of the laser spots 4 near the first edge 2and/or the second edge 7 are 130 μm.

In some embodiments, the diameters of the laser spots 4 near the midline3 range from 50 μm to 60 μm, and the diameters of the laser spots 4 nearthe first edge 2 and/or the second edge 7 range from 85 μm to 100 μm.

As can be known from the above embodiments, the method for improvingalignment between an SE and metal printing according to the presentdisclosure achieves at least the following beneficial effects.

In the method for improving alignment between an SE and metal printingaccording to the present disclosure, between the first edge and themidline, a plurality of the laser spots are arranged along a firstdirection to form spot rows, extension directions of the spot rows areparallel to an extension direction of the first edge, M spot rows arearranged along a second direction, where M is a positive integer andM>1, and the second direction intersects with the first direction. The Mspot rows include N sub-spot regions arranged along the seconddirection, where N is a positive integer and 1<N≤M, the sub-spot regionsinclude at least one of the spot rows, and areas of the laser spots ineach of the sub-spot regions are equal. The areas of the laser spots indifferent sub-spot regions are gradually increased along a direction inwhich the midline points to the first edge. The metal electrode isgenerally printed by a screen. Due to bonding of hot melt adhesive atedges of the screen and prolonging of the service life, the metalelectrode at an edge position may deviate. That is, the position of themetal electrode at the edge changes greatly, while the position of themetal electrode in the middle changes little. Therefore, by designingthe area of the laser spot at a middle position to be small and the areaof the laser spot at an edge position to be large, contact resistance ofcontact between the silicon wafer and the SE at the middle position canbe reduced, the fill factor can be increased, and efficiency of a solarcell can be improved. Besides, when the service life of the screen isprolonged, the metal electrode at the edge position and the SE at theedge position are accurately aligned.

Although some specific embodiments of the present disclosure have beendescribed in detail through examples, it should be understood by thoseskilled in the art that the above examples are for illustrative purposesonly and not intended to limit the scope of the present disclosure. Itshould be understood by those skilled in the art that the aboveembodiments can be modified without departing from the scope and spiritof the disclosure. The scope of the present disclosure is defined by theappended claims.

What is claimed is:
 1. A method for improving alignment between aselective emitter (SE) and metal printing, comprising: providing asilicon wafer comprising a first edge and a midline, wherein the midlineis parallel to the first edge; texturing and diffusing a surface of thesilicon wafer; and illuminating the surface of the silicon wafer bylaser spots to form the SE, wherein a plurality of the laser spots arearranged along a first direction between the first edge and the midlineto form spot rows, extension directions of the spot rows are parallel toan extension direction of the first edge, M spot rows are arranged alonga second direction intersecting with the first direction, and M is apositive integer and M>1; the M spot rows comprise N sub-spot regionsarranged along the second direction, N is a positive integer and 1<N≤M,the sub-spot regions comprise at least one of the spot rows, and areasof the laser spots in each of the sub-spot regions are equal; and theareas of the laser spots in different sub-spot regions along a directionfrom the midline pointing to the first edge gradually increases.
 2. Themethod for improving alignment between an SE and metal printingaccording to claim 1, wherein each of the sub-spot regions comprisesonly one of the spot rows.
 3. The method for improving alignment betweenan SE and metal printing according to claim 1, wherein each of thesub-spot regions comprises at least two of the spot rows.
 4. The methodfor improving alignment between an SE and metal printing according toclaim 1, wherein the silicon wafer further comprises a second edgearranged opposite to the first edge along the second direction; whereinthe plurality of laser spots are arranged along the first directionbetween the second edge and the midline to form spot rows, P spot rowsare arranged along the second direction, and P is a positive integer andP>1; the P spot rows comprise Q sub-spot regions arranged along thesecond direction, Q is a positive integer and 1<Q≤P, the sub-spotregions comprise at least one of the spot rows, and areas of the laserspots in each of the sub-spot regions are equal; and the areas of thelaser spots in the sub-spot regions along a direction from the midlinepointing to the second edge gradually increases.
 5. The method forimproving alignment between an SE and metal printing according to claim4, wherein the laser spots between the midline and the first edge form afirst spot region, the laser spots between the midline and the secondedge form a second spot region, and the first spot region and the secondspot region are symmetric along the midline.
 6. The method for improvingalignment between an SE and metal printing according to claim 1, whereinthe laser spots have a circular shape.
 7. The method for improvingalignment between an SE and metal printing according to claim 6, whereinprinting speeds of lasers on the silicon wafer, laser power, laserfrequencies, and focal lengths of a lens through which the lasers areemitted are adjusted to adjust diameters of the laser spots.
 8. Themethod for improving alignment between an SE and metal printingaccording to claim 7, wherein, for the laser spot far from the midline,the printing speed ranges from 20000 mm/s to 24000 mm/s, the laser powerranges from 29 W to 31 W, the laser frequency ranges from 230 KHZ to 270KHZ, and the focal length ranges from 30000 mm to 38000 mm.
 9. Themethod for improving alignment between an SE and metal printingaccording to claim 7, wherein, for the laser spot close to the midline,the printing speed ranges from 20000 mm/s to 24000 mm/s, the laser powerranges from 28 W to 30 W, the laser frequency ranges from 270 KHZ to 330KHZ, and the focal length ranges from 28000 mm to 35000 mm.
 10. Themethod for improving alignment between an SE and metal printingaccording to claim 6, wherein the diameters of the laser spots rangefrom 35 μm to 130 μm.
 11. The method for improving alignment between anSE and metal printing according to claim 10, wherein the diameters ofthe laser spots adjacent to the midline range from 50 μm to 60 μm. 12.The method for improving alignment between an SE and metal printingaccording to claim 10, wherein the diameters of the laser spots adjacentto the first edge and/or the second edge range from 85 μm to 100 μm. 13.The method for improving alignment between an SE and metal printingaccording to claim 1, wherein the laser spots have a rectangular shapeor a polygonal shape.
 14. The method for improving alignment between anSE and metal printing according to claim 1, further comprising: forminga pyramid structure on a surface of the silicon wafer during thetexturing.
 15. The method for improving alignment between an SE andmetal printing according to claim 1, wherein the silicon wafer ismonocrystalline silicon, polycrystalline silicon, or amorphous silicon.